1. Field of the Invention
The present invention relates to an integrated circuit (IC) for driving a display device, and more particularly, to an integrated graphic- and character-mixing circuit for driving a liquid crystal display (LCD) panel.
2. Description of the Related Art
Display devices have been widely applied to contemporary systems as electro-optical elements for converting electrical signals into visual images. LCD devices are an example of widely-used display devices. They can be of a graphic-type for individually displaying each pixel of an LCD panel in bit units, or of a character-type for displaying complete characters on the LCD panel as a character set. A driving circuit is tailored to serve each type of LCD device.
Referring to FIG. 1, a conventional graphic-type LCD driving circuit includes a microprocessor unit (MPU) interface circuit 101, a graphic data RAM 103, and a common/segment LCD driver 105.
The MPU interface circuit 101 is connected to an external microprocessor unit (MPU), or microcontroller unit (MCU), and is configured to transmit and receive data. The memory size of the graphic data RAM 103 corresponds to the number of pixels on the LCD screen. Data is transmitted to the graphic data RAM from the MPU via the MPU interface circuit 101. The common/segment LCD driver 105 outputs a common level signal (COM) and a segment level signal (SEG) in response to data output by the graphic data RAM 103. The COM and SEG signals in turn drive the LCD panel.
Data transmitted from the MPU to the graphic-type driving circuit generally includes a large amount of image data to be displayed on the LCD screen. It is therefore stored in an external ROM interfaced with the MPU. When the MPU reads data from the external ROM and writes the data into the graphic-type driving circuit, the circuit converts binary data of xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d into appropriate COM and SEG signals, suitable for driving the graphic LCD panel.
However, in a system employing a conventional graphic-type LCD driving circuit, when only one MPU is employed, that single MPU must read data from the external ROM and write the data into the graphic-type driving circuit each time the LCD panel is updated. Thus, the MPU is overburdened. Furthermore, the external ROM increases system costs.
Referring to FIG. 2, a conventional character-type LCD driving circuit includes an MPU interface circuit 201, a character display data RAM 203, a character font ROM 205, and a common/segment LCD driver 207.
The MPU interface circuit 201 is connected to an external MPU (or MCU) and is configured to transmit and receive data. The character font ROM 205 stores font data of a set of complete characters, for example a set of Korean characters, Chinese characters, or English alphabet characters, etc. The characters are related in size so as to occupy a specified number of pixels, for example 5xc3x978 or 16xc3x9716 pixels. The character display data RAM 203 stores addresses corresponding to font data stored in the character font ROM 205. The addresses are transmitted from the external MPU via the MPU interface circuit 201. The common/segment LCD driver 207 receives font data from the character font ROM 205 and outputs a common signal level (COM) and a segment signal level (SEG). In this manner, complete characters are displayed on an LCD panel.
When the external MPU writes the address of a character font for display on the LCD unit into the character display data RAM 203, font data corresponding to the address is output by the character font ROM 205. Thus, the common/segment LCD driver 207 displays the font data as a complete character on the LCD panel.
As described above, the conventional character-type driving circuit includes a character font ROM 205 to reduce processing burden on the MPU. However, this configuration is limited in that only characters stored in the character font ROM can be displayed, to the exclusion of graphics.
The conventional graphic-type LCD driving circuits and character-type LCD driving circuits each exhibit the limitations described above, and are therefore not amenable to use with a number of contemporary systems such as a cellular telephone systems, which require concurrent display of not only graphics in the form of pictures and image data, but also complete characters, on an LCD panel.
To address the above limitations, it is an objective of the present invention to provide an integrated graphic and character mixing circuit for driving a display device, for example an LCD display, by which an external ROM is unnecessary, wherein less burden is imposed on the associated MPU, and wherein both graphic images and complete characters can be combined and concurrently displayed on an LCD panel.
Accordingly, to achieve the above objective, the present invention provides an integrated display driving circuit, for example an LCD panel driving circuit, comprising a character font ROM, a character display data RAM, a graphic image data RAM, a property register, a character/graphic mixed display control circuit, an interface circuit, and a common/segment LCD driver.
The character font ROM stores font data related to complete characters. The character display data RAM stores addresses corresponding to the font data stored in the character font ROM. The graphic image data RAM stores graphic image data. The property register stores selection information related to the graphic and character data. The character/graphic mixed display control circuit receives the font data from the character font ROM and graphic image data from the graphic image data RAM, and selects and outputs final data to be displayed on an LCD panel, in response to the output of the property register. The interface circuit receives the addresses, the graphic image data, and the selection information from an external MPU or MCU and transmits them respectively to the character display data RAM, the graphic image data RAM, and the property register. The common/segment LCD driver generates a common signal level and a segment signal level in response to the output of the character/graphic mixed display control circuit and the common and segment signals are used to drive an LCD unit.
According to a preferred embodiment, the number of bits of the property register is determined by the size of the font stored in the character font ROM, and the LCD panel is segmented according to the maximum size of the font. When the value of each bit of the property register xe2x80x9c0xe2x80x9d, a character stored in the character font ROM is displayed on the LCD panel, and when the value of each bit of the property register is xe2x80x9c1xe2x80x9d, graphic image data stored in the graphic image data RAM is displayed on the LCD panel.